The term "pretreatment" means the treatment of wastewater by commercial and industrial facilities to remove harmful pollutants before being discharged to a sewer system under the control of a publicly owned treatment works (POTWs).

Industrial wastewaters differ in their impurities: acidic from a plating process, colorings, acids, oils and fats from food processing, or the presence of organic chemicals, such as pesticides, paints, dyes, or detergents. As industrial processes differ, so do their wastewater impurities.

Treatment can be as simple as chemical addition or as complex as the integration of multiple unit processes for a complete water treatment system. The solution can be achieved by either equipment purchase or by a service agreement where the end user does not acquire the equipment. Since there can be various combinations and permutations that create the integrated system, the final solution is one that offers the lowest possible combined capital and operating costs over a defined lifecycle.